Manufacture of asphalts



Patented Sept. 17, 1940 UNITED STATES ATENT OFFICE MANUFACTURE OF ASPHALTS tion of New York No Drawing. Application March 21, 1940, Serial No. 325,186

3 Claims.

This application is a continuation-impart of our co-pending application S. N. 129,377, filed March 6, 1937.

The invention relates to asphaltic products of 5 the kind suitable for paving and similar purposes and relates especially to methods of producing such products. The invention relates particularly to the production of such asphaltic products from petroleum.

It-is customary to define the characteristics and properties of asphaltic materials by means of measurements and ratios, such as penetration and ductility values, melting points, and temperature susceptibilities, the latter being represented by 1 the ratio of penetration at various temperatures,

for instance, at 100 F. and 77 F. or at 77 F. and 32 F. These measurements are made by standard methods of test of the American Society for Testing Materials. For example, penetration values are obtained by measuring the distance of penetration of various asphaltic materials by a specified needle loaded with a specified weight at a specified temperature for a specified time (see A. S. T. M. method No. D 5-25, Penetration of Bitu'minous Materials). Ductility values are obtained by measuring the elongation before breaking of a specified sample pulled apart at a specified speed and at a specified temperature (see A. S. T. M. tentative method No. 4, D 113-32 T, Ductility of Bituminous Materials), Melting points (softening points) are commonly determined by the ball and ring method, which consists in filling a ring with asphalt and placing a steel ball of specified weight in the center of the asphalt, and then gradually heating the asphalt by means of hot water. The melting point is recorded as the temperature at which the asphalt, under the load of the ball, touches the bottom of the Water bath (see A. S. T. M. method No. D 36-26, 40 Softening Point for Bituminous Materials). The above methods are used for the determinations given herein.

The properties represented by the above measurements are important from the standpoint of the present invention. It is important that asphaltic products employed for the purposes contemplated herein be of proper hardness, as determined by penetration tests, and that they be of low temperature susceptibility and of high ductility. Penetration is a measure of consistency and hardness, serving primarily to classify asphalts into commercial grades of various degrees of hardness. Temperature susceptibility (penetration ratio) indicates the susceptibility of a product to change of hardness with change in temperature, that is, its rate of softening. It is desirable that temperature susceptibility as expressed by the above indicated ratio be as low as possible, since, if it is too high, those asphalts which have suitable hardness for cold weather will flow and be deformed in warm weather and, conversely, those suitable for warm Weather will be too brittle for cold Weather use. Ductility is a measure of the cementing power of asphaltic material, that is, its power to hold together the aggregate or other mineral filler in the final pavement compound, and is a very desirable property, contributing extensively to the ability of pavements and similar asphaltic structures to withstand Wear, disintegration, trailic shock, and mechanical stresses clue to temperature, weathering, and the like. For example, asphalts having low duetility, when used in. paving mixtures, produce mixtures which separate and disintegrate under conditions of use, while asphalts of high ductility are capable of absorbing more filler than ordinary asphalts without objectionably impairing the mechanical strength of the mixture.

The importance of the above properties in asphaltic material may be illustrated by the specifications and requirements of the State of Texas and the city of New York which are here reproduced in part:

STATE OF TEXAS At 32 F., 100 grams, 5 sec Not less than 3 (about 15 for 32 F., 200 g. secs). 30-40, 40-50, 50-

60 or 60- as called for. At F.,100 grams, 5, sec Not more than 4 times that at 77 F.

At 77 F., 100 grams, 5 sec Ductility At 77 F., not less than 40 centimeters at 50 penetration.

Joint filler Penetration At 32 F., 100 grams, 5 sec Minimum 4. At 77 F., 100 grams, 5 sec 60-100. At 100 F., 100 grams, 3 sec Maximum 3.25 times that at 77 F. Ductility At 77 F., not less than 40 centimeters.

Up to the present time, commercial manufacture of petroleum asphalt has been largely dependent upon the fortuitous presence of desirable properties in selected crude oils for the attainment of characteristics such as described and specified above; i. e., asphaltic or naphthenic crudes or asphaltic or naphthenic residues from mixed base crudes. Such crudes, roughly in the order of their desirability, are Mexican, Venezuelan, Smackover, Californian, and Coastal. The best stocks; e. g., Mexican, can be steam refined to produce asphalts, but for those grades of asphalt requiring low temperature susceptibility, as typified by the above specifications, the stocks must be air blown. Blowing results in loss of ductility. This tendency sometimes may be minimized to a limited extent by careful operation, but with a great many residual oils capable of being converted into otherwise desirable asphalts by blowing, no amount of care will serve to produce products of desirable ductility. In order to obtain satisfactory ductility in asphalts requiring low temperature susceptibility, resort must be made to a very careful selection of crudes, even among the best Mexican and Venezuelan stocks, it being almost impossible to produce desired grades from domestic crudes.

It is an important object of the present invention to produce from commonly available petroleum stocks asphalt products which combine the above described desired properties, such as high ductility and low temperature susceptibility, and which are especially suitable for use in road surfaces and the like. It is an object to produce petroleum asphaltic products to meet specifications as desired without dependence upon the use of particular natural asphaltic stocks of specially selected quality. These objects are accomplished, and a novel product is produced, by a simple low cost novel process.

In accordance with the present invention, asphalt products having desirable properties as above described can be produced from certain classes of petroleum products or derivatives having asphaltic constituents by adjustment and control of the character and amount of their oil content, in relation to their asphaltic properties, according to the principles described below. For example, asphaltic products having desirable properties, as above described, can be produced 1937 now U. S. Patent 2,120,377. Further asphaltic products having the desirable properties, as above described, can be produced by first mixing the solvent tar and oil of relatively high V. I. and then converting the mixture. This latter specific phase of the present invention is disclosed and claimed in the co-pending application S. N. 66,823, filed March 3, 1936 now U. S. Patent 2,120,376. In the present invention we have found that certain other bituminous materials may be used, as well as solvent tars, to produce the above mentioned desirable asphaltic products by either first converting'the bituminous material and then adding the oil of relatively high V. I., or by first mixing the bituminous material and oil of relatively high V. I. and

then converting the mixture.

According to the present invention bituminous materials in general may be employed which have an asphaltic content of good ductility characteristics and an oil content of low V. I. oil. In our process the low V. 1. oil is converted to asphaltic matter and is replaced by the addition of oil of higher V. I. whereby temperature susceptibility is greatly improved, 'i. e., lowered. Since oil of low V. I. will be converted before oil of high V. I., the process may be carried out equally well, as stated above, by adding the high V. I. oil before the conversion step. The selected bituminous material should have an asphaltic content of good ductility characteristics when carrying an appreciable oil content, and, therefore, one phase of the invention maybe practiced by converting the bituminous material to apparent loss of ductility before adding the oil of high V. I., whereupon the oil will restore the high ductility to the asphalt as well as reduce its temperature susceptibility. Besides solvent tars, the class of bituminous materials to. which our present invention is applicable includes certain natural asphalts; asphaltic residues and the like, unconverted, blown or steam refined; and certain pressure tars. If a stock is selected which has already been converted, e. g., steam refined asphalts of high ductility, such as Californian, and the like, the invention may be practiced by merely adding the oil of high V. I. Thus it will be seen the invention can be applied to improve temperature susceptibility of stocks in general which are capable of furnishing asphalts having sufiicient ductility.

It has been proposed to make asphaltic products by blowing solvent tars, for example, but asphalts so produced are dependent for their properties upon the character of the tar employed,the same as asphalts have been dependent upon the character of the crude oil used,and solvent tar asphalts as a class are characterized by notably poor temperature susceptibility and are therefore inferior and unsuitable for the uses contemplated herein. It has also been proposed to precipitate relatively oil-free bitumen from petroleum residues or petroleum asphaltic products with a precipitant such as propane, and then add back to the precipitated bitumens oils of desired properties to produce asphalt products. This process is complicated, slow and costly.

The present invention, on the other hand, produces asphalts of good properties, controlled as desired, including high ductility, good (low) temperature susceptibility, and good penetration, and accomplishes thiswithout necessity of removing any portion of the material by costly steps of solvent precipitation, vacuum distillation, or the like.

iii

In the present invention a portion of the oil con- 75 tent of the solvent tar or other bituminous material is removed by conversion into asphaltic material by blowing or steam refining, which is less expensive than removal by solvents or precipitants, increases yield of asphalt, reduces oil content, and effects such reduction in oil content by getting rid of the highly naphthenic portion of the oil content which would be the most objectionable in the asphalt and is not wanted. That is, in the-present invention, and contrary to what occurs when propane precipitation is employed, the more naphthenic portions of the oil content of the tar are removed first by conversion into asphaltic material, the unconverted portions being less naphthenic and therefore more desirable in the asphalt. This increases yield and improves temperature susceptibility by improving the V. I. of the remaining oil content of the asphalt. Temperature susceptibility is then further improved by adding additional oil of appropriately high V. I. This invention also makes it possible to take advantage of the high ductility characteristic of solvent tar asphalts, or similarly endowed bituminous materials, and at the same time and at low cost to combine this property with good temperature susceptibility in a finished asphalt.

With respect to solvent tars, the preferred classes thereof, suitable for the uses of this invention, are naphthenic tars resulting from the single or double solvent extraction of long or short residuums from asphaltic or mixed base crudes, employing naphthenic solvents of the class typified by cresylic acid, phenol, furfural, nitrobenzene, sulfur dioxide, and the like, or the substantial'equivalent of such'tars. However, although it is preferable to utilize solvent tars of relatively high asphaltic content and less asphalt tars are relatively less useful, less asphaltic tars can be used to some extent and also can be reduced, by distillation to obtain useful residues of fairly high asphaltic content, and can then be exposed to the steps of the process described herein. It is the class of solvent tars defined herein that is covered by the terms as used in the claims. These tars are not the same or equivalent to propane precipitated bitumens. These solvent tars normally and preferably contain some asphaltic matter before blowing; i. e., asphaltenes and resins. They also contain oil. The greater proportion of the oil content of the tars is highly naphthenic and readily forms asphaltic matter upon blowing. The most naphthenic portions; i. e., the oil that would be the most undesirable in the finished asphalt, is the most unstable and therefore is the first to be removed by conversion upon blowing. The oils contained in solvent tars have very low viscosity indices, as they include a large proportion of highly naphthenic constituents. The viscosity indices of these oils are far below zero on the standard 0-100 viscosity index scale. It is the presence of these highly naphthenic or low viscosity index oils which to a great extent imparts a high temperature susceptibility to asphalts derived from solvent tars. In the present invention the oils present in solvent tars are selectively converted and/or removed by blowing the tars with air or other oxidizing gas to a controlled extent, followed by addition of oil of better V. I. which in all cases should be above zero V. I. By proceeding in this manner the most undesirable naphthenic constituents are removed while the more paraffinic oils remain, thereby producing an oil content of improved viscosity index.

The oil content of the solvent tars is, as stated, so highly naphthenic that the blowing operation is in itself not capable of producing an asphalt of sufficiently low temperature susceptibility. It is therefore an important step in the present invention to add suitable amounts of relatively paraffinic oils to the blown tar; i. e., oils of relatively high viscosity index as compared with the original oil content of the solvent tar. The quantity and degree of paraifinicity of these added oils can be varied with the result that the process can be easily controlled both as to extent of blowing'an'd the amount and character of oil addition. Ordinarily the added oil will have not only a higher viscosity index than. that of the oil originally present in the tar, but will have a viscosity index higher than that of the improved oil remaining in the tar after the blowing treatment. Because of the extremely low V. I. of the oil content of the solvent tars, good temperature susceptibility improvement can ordinarily be obtained with diluent oils ranging down to zero V. I. The viscosity of the oil added to the solvent tar does not materially affect the quality of the final asphalt, but light oil, just passing flash point requirements and the like, is ordinarily used, because such oil is cheaper than more viscous oil and less of it is required to bring the asphalt to proper penetration.

The selected bituminous material may be blown to any suitable extent, as desired, but is preferably blown to a point beyond the penetration and/or melting point specifications desired in the finished asphalt, and is then brought back to the desired or specified values by adding oil of proper viscosity index characteristics, which causes a definite improvement or lowering of the temperature susceptibility for the specified penetration value or melting point. The blowing is conducted at elevated temperatures, say 400 F.- 500 F., in the known manner of asphalt blowing. As a specific example of this manner of proceeding, a solvent tar may be blown to a penetration value of at 77 F., and may then be out back with a suitably high viscosity index oil to lower the temperature susceptibility and raise the penetration value to commercially useful grades, the hardest commercial grade having a penetration value of about 40 at 77 F. The solvent tar may be blown to the point of apparent loss of ductility, i. e., to a point where the ductility is so low that it records as zero on the ductility testing machine, and then the ductility and penetration values can be raised by the addition of the oil of suitably high viscosity index. In such a case, the upper limit of hard blowing is where the ductility is too low even after adding the oil to the blown tar, which ordinarily occurs when the tar is blown to a melting point of about 220 F.

By practice of the present invention using properly selected materials as set forth herein, we are able to produce asphalts quite easily that meet required specifications such as 40 cm. ductility at 77 F. and temperature susceptibility of 4.0 or 4.5 at 77 F. and 32 F. (penetration 77 F., 100 g., 5 secs. divided by penetration 32 F., 200 g., 60 secs.) or more rigid specifications. In fact in most of our operations the ductility produced is around 100 cm. at 77 F. and the temperature susceptibility at 77 F. and 32 F. is 4.0 or lower.

We claim:

1. The method of producing an asphaltic product of relatively low temperature susceptibility and high ductility which comprises selecting a bituminous material comprising a substantial amount of asphaltic matter and oil of relatively low viscosity index and. which may be converted alone to produce an asphalt of high temperature susceptibility and a ductility above about cm. at 77 F., converting oil of low viscosity index in said bituminous material to asphaltic matter to produce an asphalt of high temperature susceptibility and then adding to said converted bituminous material a sufficient amount of an oil of higher viscosity index than said converted oil and in all cases above zero viscosity index, to produce an asphaltic product having a temperature susceptibility appreciably lower than Would be possessed by the bituminous material if converted alone and a ductility above about 40 cm. at 77 F.

2. The method of producing an asphaltic product of relatively low temperature susceptibility and high ductility which comprises selecting a bituminous material comprising a substantial amount of asphaltic matter and oil of relatively low viscosity index and which may be converted; alone to produce an asphalt of high temperature susceptibility and a ductility above about 40 cm. at 77 F., converting oil of low viscosity index in said bituminous material to asphaltic matter to produce an asphalt having high temperature susceptibility and apparent loss of ductility and then adding to said converted bituminous material a sufiicient amount of an oil of higher viscosity index than said converted oil and in all cases above zero viscosity index, to produce an as phaltic product having a temperature susceptibility appreciably lower than would be possessed by the bituminous material if converted alone and a ductility above about 40 cm. at 77 F.

3. The'method of producing an asphaltic product of relatively low temperature susceptibility and high ductility which comprises selecting a bituminous material comprising a substantial amount of asphaltic matter and oil of relatively low viscosity index and which may be converted alone to produce an asphalt of high temperature susceptibility and a ductility above about 40 cm. at 77 F., mixing said bituminous material with oil of higher viscosity index than a. substantial amount of said oil in said bituminous material and in all cases above zero viscosity index, the amount of said higher viscosity index-oil being sufficient to give the mixture upon conversion a lower temperature susceptibility than would be possessed by the bituminous material if converted alone, and then converting said mixture to an asphaltic product having a ductility above about 40 cm. at 77 F. and a temperature susceptibility substantially lower than Would'be possessed by the bituminous material if converted alone.

VLADIMIR L. SHIPP. ARTHUR H. BOENAU; JAMES W. RAMSAY. 

